The need for tactile sensors distributed over the whole body has been increasing in the field of robots and humanoids. Whole body tactile sensors are tactile sensors that make it possible to provide tactile sense to the whole of a system. Most of research regarding tactile sensors relates to single sensor characteristics. The target of the research is how to detect characteristics for fineness of hand such as smooth or rough. The research is also taking place into how to give an input interface of a computer a sense of touch. According to most of the tactile sensor research in the related art, importance has been placed on the characteristics obtained. However, from the point of view of implementation of tactile sensors, application to the appropriate curved shape, ease of manufacture and ease of adjusting the mounting region are desired.
In addition to the field of robotics, tactile sensors are also desirable in the field of medicine, health and welfare, for measuring pressure distribution for the surfaces of chairs and beds, etc. This is for utilization in product development such as investigating comfort, etc., monitoring of patients, and for motion measuring and rehabilitation. In this kind of case also, a pressure distribution sensor capable of application to curved shapes is useful.
In order to implement a distributed tactile sensor, it is necessary to enable application to curved surfaces and to bring about countermeasures for problems with respect to wiring. Moreover, it is necessary to enable adjustment of mounting regions because the size and shape of the mounting region differs according to the system mounted on. However, there are no conventional tactile sensors that simultaneously satisfy all of the requirements of application to curved surfaces, problems with respect to wiring and adjustment for the mounting region while sufficiently taking into consideration manufacturing methods and costs.
When mounting tactile sensors on a system, a flexible substrate may be used in order to reduce wiring costs. In this regard, according to the related art, the arrangement of pressure sensors on the substrate is fixed, and density adjustment is not possible. Further, pressure sensors such as pressure-sensitive rubber etc. can only measure pressure in the vicinity of the sensor. The detection range therefore has to be broadened by changing the size of the pressure sensors in order to change the density. Individual products are therefore required to achieve density adjustment and cost increases are incurred.
When wiring the pressure sensors individually, the amount of wiring increases dramatically. A matrix type wiring system is therefore typically used that is capable of managing n×m pressure sensor signals using n+m wires. In this case, each sensor shares n vertical wires and m horizontal wires. This gives a substrate shape that consists of a one piece region overall. As a result, even when a flexible substrate is used, and even if application is possible to simple curved surfaces such as with a cylindrical shape, application to complex curved surfaces such as the shoulders or elbow of a robot is difficult.
In the related art, when tactile sensors are used in non-stationary regions such as the shoulders or elbow of a robot, products are custom-designed in line with the shapes of the individual regions. This is mainly caused by the size and shape of the regions the tactile sensors are to be mounted on changing substantially depending on the target. In this respect, there are therefore no conventional tactile sensors that take into consideration adjustment of sensor mounting regions after production.
Various pressure sensors exist such as pressure-sensitive resistors, capacitance-type pressure-sensitive elements, and piezoelectric elements. However, when such elements are adopted, there is no ability to provide interpolation with properties that can be calculated from a ratio of two sensed quantities for pressure acting between two pressure sensors. This means that a large number of sensors are required to increase resolution. In this respect, according to the pressure sensing method disclosed in patent document 1, light is emitted by light-emitting elements to light scattering elastic material that scatters and reflects light, with the amount of light scattered/reflected then being measured using light-receiving elements. This is based on the theory that when pressure is applied to a light scattering elastic member which scatters/reflects light, the amount of scattering/reflection changes with deformation and it is therefore possible to measure the amount of pressure. Hereinafter, this is referred to as the light-scattering type pressure-sensing method. When pressure is applied to a certain point of a light-scattering elastic member, the influence of the deformation extends from the pressure point to a point a certain amount away from the pressure point. This means that it is possible to detect pressure at a set of a light-receiving element and a light-emitting element at a certain distance away from the pressure point. The influence of the changes in pressure becomes smaller further away from the pressure point. When pressure is then applied to a point between two points where measurements are carried out by two sets of light-receiving elements and light-emitting elements, it is possible to know which point between the two points is being subjected to pressure from the ratio of pressure values for the two points measured. Further, it is also possible to estimate this pressure value from the sum of the pressure values for the two points. From the above theory, it is clear that interpolation can be implemented by the light-scattering type pressure-sensing method. Further, the light-scattering type pressure-sensing method has the feature that sensitivity adjustment can be achieved in a straightforward manner by changing a light-scattering elastic member that scatters/reflects light. However, in the case of the mounting method using optical fibers disclosed in Japanese Patent Document 1, there is the problem that compactness and automation of manufacture is difficult.
As foregoing, tactile sensors of the related art employing a flexible substrate for wiring have the following disadvantages.
(1) Different products are required for both the wiring substrate and the pressure sensors when a different density is required.
(2) Adjustment of the mounting region after manufacture cannot be considered.
(3) Products with different sensors according to sensitivity are necessary when different sensitivities are required.
(4) A wiring substrate can only be applied to simple curves.
    Patent Document 1: WO 99/04234 (U.S. Pat. No. 3,653,284)    Patent Document 2: Japanese Unexamined Publication No. 64-16902